Field
The present inventions relate to a system and method of utilizing a switch with a highly linearized resistance via bootstrapped features.
Description of Related Information
Switches such as Field Effect Transistor (FET) switches and Micro-Electro-Mechanical (MEM) switches are used in applications ranging from transmit/receive to Radio Frequency (RF) applications. One problem, is that when the input signals to the switch are near the power supply rails, the gate drive on the switches is reduced causing the resistance across the switch to increase. One solution to avoid this problem is to add a resistor in series with the gate of the switch so that when the input swings high, the gate also swings high from capacitive coupling, and the same gate drive is maintained as shown in patent US 2010/0013541-A1. However, the problem with this configuration is that during slow transients, the gate will not hold the bootstrapped voltage since there is a resistor connected. The voltage will quickly decrease to the original value as charge from the gate capacitance discharges through the resistor. In the case of a transmitter/receiver for transmit pulses of different durations, the resistance across the switch will change, and consequently the harmonic distortions will be affected. Hence, this topology does not work for transient signals with a long period. The innovations herein overcome this difficult and important issue. In particular, for high voltage transmit/receive switches used in ultrasound applications, it's especially difficult to have linearity because the input signals could be in the 100V to 200V range and it is difficult to maintain linearity over this range. Again the innovations herein invention can overcome this problem. Another problem with high voltage signals is that high voltage coupling back onto the gate could damage circuitry connected to that node. Here, the present innovations allow protection to limit the voltage at that node.